In the manufacture of a tooth crown or the like dental appliance custom-made for fixed permanent securement to a prepared natural tooth, an impression is taken of the prepared natural tooth in a pliant material and a model of the prepared natural tooth is then made by molding a hardenable material in the impression which functions as a mold. Such a model is sometimes otherwise referred to as a die, a master die, or a tooth replica, the term "model" as used herein being intended as generic to all such models, dies, master dies and tooth replicas. With such model having been made, the conventional practice is to form a wax coping on the model, invest the wax coping in an investment material, melt out the wax after the investment material has hardened thereby to form a mold cavity, and then mold or cast the dental crown in the mold cavity. A disadvantage to this method is that no matter how accurate the definition of the model is in precisely duplicating the shape of the prepared tooth, some of the definition is lost in transference of the shape to the investment material by way of the wax coping. U.S. patent application Ser. No. 103,647 filed Dec. 14, 1979 discloses and claims a method for making ceramic dental crowns and the like dental appliances wherein the model itself is used as a wall of the mold cavity thereby eliminating any loss whatsoever of definition in the construction of the mold cavity. The method of the present invention is advantageous for the preparation of tooth models for the older conventional method and for the method of the aforementioned patent application, but especially for the latter.
Tooth models have heretofore been made of epoxy resins; however, the disadvantage has been that during the curing of the epoxy resins to hardness there is some shrinkage to the end that the resulting model is not an exact duplicate of the prepared natural tooth but instead is reduced in size. The method and epoxy resin formulation of the present invention correct this deficiency to the end that by the practice of the invention tooth models can be prepared which are not only strong and hard but which are also of precisely the shape and size desired.